Read the Passage carefully and answer the Questions.

Carbonyl compounds such as aldehydes, ketones, and carboxylic acids play an important role in the biochemical process of plants and animal kingdom. Many aldehydes and ketones find applications in dye, perfumery and other industries. The carbonyl carbon atom is $sp^2$-hybridized forming three sigma and one pi-bond with oxygen. C-O bonds are polar bond due to high electronegativity of oxygen than carbon. Hence the carbonyl carbon behaves as an electrophilic center and oxygen as a nucleophilic centre. Primary and secondary alcohols yield aldehydes and ketones respectively upon oxidation with variety of oxidizing agents. The boiling points of aldehydes and ketones differ from hydrocarbons and ethers. Aldehydes and ketones undergo nucleophilic addition reaction due to presence of electrophilic carbonyl carbon. Nucleophile and a proton add across the carbon oxygen double bond.

Identify the product Y in the following reaction

$CH_3CH=CHCHO$

The correct answer is Option (2) → $CH_3CH=CHCHO$ **

The reaction shown is the oxidation of an unsaturated primary alcohol using Pyridinium Chlorochromate (PCC).

$CH_3​−CH=CH−CH_2​OH\overset{\text{Pyridinium Chlorochromate​}}{\longrightarrow}Y$

Analysis of the Reaction

1. Starting Material: The reactant is But-2-en-1-ol ($CH_3​−CH=CH−CH_2​OH$).
• It is a primary alcohol ($–CH_2​OH$).
• It contains a carbon-carbon double bond (C=C).
2. Reagent: Pyridinium Chlorochromate (PCC) is a mild and selective oxidizing agent.
3. Function of PCC:
• PCC oxidizes primary alcohols ($R−CH_2​OH$) to aldehydes (R−CHO).
• Crucially, because PCC is used under anhydrous conditions (usually in dichloromethane (DCM)), it is selective and stops the oxidation at the aldehyde stage, preventing further oxidation to a carboxylic acid.
• PCC typically does not oxidize or affect the carbon-carbon double bond (C=C) in the molecule.

Identifying the Product Y

The primary alcohol group ($–CH_2​OH$) is oxidized to an aldehyde group (–CHO), while the carbon-carbon double bond remains intact.

$CH_3​−CH=CH−CH_2​OH\overset{\text{Pyridinium Chlorochromate​}}{\longrightarrow}CH_3​−CH=CH−CHO$

The product Y is But-2-enal (also known as Crotonaldehyde).